"In a free country, when the government takes a life it matters to our community how we respond," Ogg said.
Cameron Brewer is charged with aggravated assault by a public servant for the death of Danny Ray Thomas.
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In March, Thomas was reportedly acting erratically and "foaming at the mouth" on a road in north Harris County.
Dashcam video from the incident showed Thomas approaching Brewer's patrol car with his pants down. Then, moments later, shots were fired.
Deputies say an internal investigation showed Brewer did not properly follow the sheriff's office's use of force policy when he shot Thomas to death.
Thomas' family says he was "holding some pain deep down" after his kids were drowned in a bathtub by their mother, Sheborah Thomas, in 2016.
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"He was depressed about his kids. He was going through something, as we all go through, and we all deal with stress and depression differently," said Marketta Thomas.
During Thursday's press conference, Ogg said the Harris County District Attorney's Civil Rights Division presented a thorough review of the evidence regarding the case, and presented it to a grand jury.
"Law enforcement officers have very, very difficult jobs. They perform them well almost all of the time, but in this case the deputy exceeded his lawful use of force. He disregarded his training, and a man who was innocent died," Ogg said.
Brewer is facing five to 99 years or up to life in prison if he's found guilty.
SEE MORE:
DA announces former Harris County deputy charged in deadly shooting of unarmed man
HPD: Dashcam shows deadly deputy-involved shooting of unarmed man in Harris Co.
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More details released in deadly deputy-involved shooting
Suspect killed in deputy-involved shooting in north Harris County
Suspect killed in deputy-involved shooting in north Harris County
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